As a snowboard instructor myself Id recommend the Rossi or the Dose. Just because your weight more closely corresponds with the 159cm board than the 155cm.
The Dose has an advantage because it provides a little bit more flex and is more forgiving when traveling down hills, vs the Rossignol.
Burton LTR programs are nice and convenient but they also cost money. Which alot of people do not have. I quite often provide friends with free lessons outside of my classes just to get people on the hills.
Here is a short list of ways to get going.
1. make sure you know how to push. This isn't usually the first thing on a new riders mind but it helps.
Determine your lead foot, Strap in a foot and push with your back foot. Whichever feels more comfortable is a good place to start. Work on pushing around the flats for a little while to get comfortable with the feeling of moving sideways.
2. Since I imagine the lift wont be a problem to get on, I find skiers have the hardest time getting off the lift because they tend to turn their bodies while they come down the transition. As you come to the end of your chair lift ride straighten your board, youll have to sit a little sideways but thats ok, when the chair slows down and your board touches the snow, find the board with your back foot, make sure you have it seated and stand up. Keep your shoulders in line with the direction of your board and youll coast in a straight line.
3. First thing to work on is always stopping. Fortunately the same motion that goes into stopping is also the same motion used for turning. Strap in both feet and position yourself so your facing down the hill. Your board should be perpendicular to the hill grade. Stand up and find your balance, Work your toes like a gas pedal, when you lower them youll move forward, when you raise them youll come to a stop. Continue to do this until you reach the bottom.
4. When your on top of the hill again, get in the same position. Stand on your heel edge, and work on the gas pedal motion again, this time work on shifting your weight from foot to foot. This will cause you to "leaf" back and forth across the hill. This is the first step to turning, this motion gets you used to controlling your board so that you are familiar with how your board reacts to your weight change.
Thats about all I usually fit into an hour lesson for beginners, When you get more comfortable you can load your lead foot with weight and it will begin to point down hill, When you do this make sure your weight is either centered or forward. and to slow down its a combined motion of rotating your shoulders, leaning onto your heels and shifting your weight as the board turns. But dont get ahead of yourself. take it nice and slow, make sure to get helmets and as someone already mentioned never put your hands down when you fall. try to fall on your forearms as a sprained wrist is never fun.